Either way, there isn't a massive need for a direct Blackpool to Manchester Airport service if it's operationally more convenient to connect it to somewhere else, provided Airport services remained on the corridor more widely (which 2tph of them would).
If you're talking Chinese and US tourists, they aren't going to be flying to Manchester in huge numbers. They'll fly to Heathrow, "do" London* first, then use Avanti West Coast (or HS2) to get to their preferred bit of the North West. Meanwhile, European tourists wanting to visit Liverpool will just use sleasyJet or Eireflop to fly to Speke instead.
UK regional airports are more for British people flying other places than tourists coming in.
* And Oxford, Stratford etc.